Due to environmental concerns as well as increasing population, environmentally friendly and efficient power generation systems are desired. While there have recently been advances in systems that utilize renewable resources, such as solar power, wind, geothermal energy, and the like, efficiencies of such systems trail conventional turbine-based power generation systems, and costs of building such systems are relatively high. Moreover, generally, systems that utilize renewable resources output variable amounts of electrical power depending upon environmental factors, such as cloud cover and wind speeds.
Supercritical Brayton cycle power generation systems have been proposed and theorized as efficient power generation systems. Advantages of supercritical Brayton cycle power generation systems include the utilization of an environmentally friendly, naturally occurring compound such as carbon dioxide. Additional advantages of supercritical Brayton cycle power generation systems include a relatively small footprint when compared to conventional turbine-based power generation systems. Moreover, supercritical Brayton cycle power generation systems have been theorized to have efficiencies that meet or exceed efficiencies of conventional power generation systems.
Supercritical Brayton cycle power generation systems offer a promising approach to achieving higher efficiency and more cost-effective power conversion when compared to existing steam-driven power plants, and also perhaps gas turbine power plants. A supercritical Brayton cycle power generation system is a power conversion system that utilizes a single-phase fluid operating near the critical temperature and pressure of such fluid. Generally, two types of power conversion cycles have been proposed: a recuperated Brayton cycle and a recompression Brayton cycle. Other types of power cycles, such as a power take off cycle, cycles with reheat or inter-cooling, split-flow compressor discharge cycles that heat a fraction flow rather than recuperate it, or cycles that feed all or a portion of the high pressure flow directly to a turbine while the low pressure flow leg provides the heating can also be utilized, wherein such cycles employ a Brayton cycle.
A problem for open cycle heat sources in recompression closed Brayton cycles (RCBCs) is that while the recompression cycles may be very efficient, the cycle does not extract very much heat from the open cycle heat source. For example, the heat source flow may come in at 900° C., and only be reduced to 700° C. at the discharge of the heating heat exchanger. There is a great deal of energy NOT being extracted from the heat source flow by the RCBC. And this is because the recuperation in the RCBC is so efficient that the fluid entering the heater is very hot.
A need remains, therefore, for an RCBC system and method of operation that extracts as much heat from the heat source stream as is economically reasonable. This invention applies the design characteristics of RCBC's in such a way as to meet this need. In general, the concept applies separate RCBC flow paths at the high temperature portion of the system, and retains the single recompression flow path to each of the two compressors. The result is a cycle that capitalizes on the efficiency benefits of RCBC technology while still extracting as much heat from the heat source stream as is desired